Thin film deposition is a vital aspect of semiconductor manufacture. In order to produce an integrated circuit, thin films of various materials are used as barriers to the diffusion or implantation of impurity atoms, or as insulators between conductive materials and the silicon substrate. Typically, holes or windows are cut through the barrier material wherever impurity penetration or contact is required.
A mask is used to form the necessary pattern or windows or holes on the surface of the silicon substrate. The patterns are first transferred from the mask to a light-sensitive photoresist. Chemical or plasma etching is then used to transfer the pattern from the photoresist to the barrier material on the surface of the silicon substrate. Each mask step requires successful completion of numerous processing steps.
Metallization of electronic components, such as integrated circuits, to produce electrical contacts in integrated circuits is an important step in the manufacture of these devices. Metallizations are performed by depositing the metal uniformly followed by the forming of a pattern through the use of masking and etching steps. Existing technology involves the deposition of aluminum for MOS devices and PtSi, Ti, W, Au, and TiN for bipolar devices. The deposition is accomplished by evaporation of the metal or by sputtering of the more refractory materials.
Lasers have been used to form deposits by reacting with a vapor species which undergoes decomposition so as to deposit a metal on the substrate. U.S. Pat. No. 4,496,607 to Mathias describes a laser process for producing electrically conductive surfaces on insulators in which a laser beam is used to melt tracks onto a substrate. The tracks receive conductive particles to result in the formation of computer controlled patterns designed according to tracings characteristic of those used in circuit boards.
U.S. Pat. No. 4,372,989 to Menzel describes a method of producing metal and alloy films in which a laser beam is used to irradiate the surface of a metallic layer. The laser beam is used to change the metallic layer from amorphous to monocrystaline.
FIG. 1 is a schematic view of a prior art laser writing apparatus, as described in an article entitled "Laser Microfabrication Technology and Its Application to High Speed Interconnects of Gate Arrays" by Anthony F. Bernhardt, et al., Materials Research Society Symposia Proceedings, 76, 223-234 (1987). As seen in FIG. 1, an optical system 10 is used for scanning a focused argon-ion laser beam (514.5 .ANG.) 12 emanating from a source 14 across a wafer 16. The wafer 16 is housed in a reaction vessel 18 into which reactant gases are introduced. A mirror 20 directs the beam 12 through a power modulator 22 and beam conditioning optics 24. Mirrors 26 and 28 then deflect the beam 12 to two acousto-optic crystals in deflector 30. These deflect the beam in orthogonal directions to allow short distance (0.5 mm) translation of the laser focus without mechanical moving elements.
Relay optics 32 image the deflected beam through a microscope objective 34, which passes the focused beam through a window 36 and into the reaction chamber 18. The objective 34 focuses the beam to an approximately one micron scanning spot on the wafer 16 within the roughly 500.times.500 micron scan field of the deflector 30. The reaction vessel 18 is mounted on a motorized X-Y stage 38, which is computer controlled, to move the wafer 16 between the 500 micron scan windows. During laser writing, the deposition and etching microreactions are followed through an optical microscope 40 and video camera 42.
Basically, the apparatus according to FIG. 1 is used in a system where the precursor is present as a species in the vapor phase above the substrate. The very high temperatures generated in a very small area cause deposition of either silicon or nickel. This type of laser writing through the pyrolysis of a vapor species is limited to very few systems. The particular system involving nickel carbonyl is not attractive because this chemical is very hazardous. Moreover, control of deposition parameters is more difficult when the precursor is in the vapor phase.